Well, that’s just the point! There is no “best”.
Or worst. (Well, for the sake of argument!)
You’ll find that a discussion of whistles can run like this:
“Yeah, I have a Copeland, sterling silver. Never heard anything better in all my life!”
“Ah, sure. I had a Copeland too. Sterling. Beautiful to look at, but sounded like shyte. Sold it and went back to my old Generation. Never heard anything better in all my life!”
I have a Becker low D, and a bamboo low D, both I can finger more or less with a piper grip & using my little finger on right hand,
but on both models, there is fipple issues I think, because the tone seems a little quiet or has other issues. I want to avoid those issues
if I buy another whistle, and I also would like to perhaps make it easier to cover the finger holes, but that is a secondary issue.
I am asking which of the three is better?[/quote]
I see — thanks for clarifying!
Never heard of Becker. Bamboo is often hit or miss. Loads of touristy type whistle-like objects.
Again, as for which is “better”, I think the only one who can really answer that is you. After all, what I find “better” isn’t even on your list! 
I know for me, I don’t care too much for Susato whistles in general. (Don’t really like plastic, for one; tone / sound / volume were not my cup of tea.) Never owned or tried any of the others.
As for low Ds, I have a Copeland that I really like. Didn’t care too much for the Overton or the MK that I had. Shaw I like too. And Asarkar. I don’t have any trouble with fingering any of those three without pipers gymnastics. Mind you, Copeland and Shaw are both conical, so finger holes are more closely spaced.
YMMV and I’m sure that you’ll get at least a dozen different opinions from the next three people to respond!